EVOLUTION AND THERMODYNAMICS 



increase of entropy in another part. The two parts must, of course, 

 be interlinked by some sort of action, e.g. radiation. The essential 

 ph3^sical meaning of increase of entropy is a loss of power of spon- 

 taneous action. Two bodies at different temperatures automatically 

 tend to come to a common temperature, but having done that they 

 stop doing anything. It is the same with matter at different levels 

 (subject to the law of gravity), electricity at different potentials, and 

 so on. The tendency is always to come to a state of passivity, and 

 whenever such a tendency takes effect, entropy increases. The "run- 

 ning down" of the world is therefore a drift towards a state of relative 

 quiescence. 



From the point of view of other sciences and of the human world- 

 view in general, it is important to note exactly what words the physicist 

 uses to describe his improbable order and his probable disorder. If 

 we turn to the writings of the American mathematical physicist, 

 Willard Gibbs, the first among the great founders of thermodynamics, 

 we find that he only uses one "ordinary" word to describe high 

 entropic states, namely "mixed-up-ness."^ This does not occur in any 

 of his published writings, but only as the title of a paper which he 

 had intended to write, and which was found among a list of such 

 titles among his papers after his death. The opposite of "mixed-up- 

 ness" is separatedness. 



Later on, however, the practice grew up among physicists and 

 astronomers of using the term "organisation" for pre-entropic states. 

 Eddington has been a protagonist of this use, as the following passages 

 from his Nature of the Physical World s\\.ow. 



"We have to appeal to the one outstanding law, the second 

 law of thermodynamics, to put some sense into the world. It 

 opens up a new province of knowledge, namely, the study of 

 organisation; and it is in connection with organisation that a 

 direction of time-flow and a distinction between doing and un- 

 doing appears for the first time."^ 



Or again: 



"Let us now consider in detail how a random element brings 

 the irrevocable into the world. When a stone falls it acquires 

 kinetic energy, and the amount of the energy is just that which 

 would be required to lift the stone back to its original height. 



^ Collected Scientific Papers of J. Willard Gibbs (London, 1906), p. 418. 

 ^ The Nature of the Physical JVorld, p. 67. 



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